EPOW - Ecology Picture of the Week

Orbweaver With Missing Legs

Golden Orbweaver (Nephila cf. pilipes), Family Nephilidae
Bali, Indonesia

Explanation:  It is obvious:  this spider has only six legs.  What? How?

This is a golden orbweaver, a female given the immense size.  The species is very widespread in south and southeast Asia, ranging to Australia and Oceania.  

I found this female specimen while visiting the Tirta Sudamala Purification Temple on the island of Bali in Indonesia.  The male, usually a diminutive partner, was nowhere to be found; he likely already provided his mating service and was slain or even consumed by the female.   

But ... six legs?  Species of insects (arthopods of Class Insecta) are well-known to be six-legged, with spiders (arthopods of Class Arachnida) having eight legs.  At times, yes, spiders can lose legs to predators, or perhaps from genetic defects.  We have encountered other golden orbweavers with only seven legs, such as this one in northeast India, and others can be found on-line such as in Australia.  

This female seemed otherwise healthy and robust, and was guarding her web, perhaps in wait of wary flying insects for dinner.  

I thought perhaps that the great asymmetry to her body mass would have caused her to weave a very asymmetric web, but, as I show in the following photo, that did not seem to be the case.  

Hmmm.  Perhaps she recently lost the legs after weaving the web ... or, such a loss of major limbs does not impede the correct, symmetric web-weaving behavior.  I would find no studies on this.  Or how the loss of legs, particularly these two, might impact their predation and feeding behavior, or not.  That would be an interesting study in itself.

After a further (but not exhaustive) search of some of the scientific literature, the only clue I found is a study (Neumann and Schneider 2020) of another species of spider (one that is "sexually cannibalistic" as are at least some orbweavers) where the males (not females) "sacrifice" legs to passive aggressive females.  But how that might pertain here is not clear; perhaps this female let a leg or two go during some predator attack.  
  

     So the mystery continues...

Information:
            Neumann, R. and J. M. Schneider.  2020.  Males sacrifice their legs to pacify aggressive females in a sexually cannibalistic spider.  Animal Behavior 159:59-67.